As a functional oligosaccharide, raffinose is widely existed a variety of natural products, and standard naming is beta-D-fructofuranosyl D-galactopyranosyl-(1→6)-D-glucopyranoside. It is non-reduced sugar, composed by galactose, glucose and fructose, with the following structure form:

Raffinose was deemed anti-nutritional factors on the grounds that lack of α-galactosidase in humans. Raffinose cannot be decomposed and absorbed in the small intestine, so it is accumulated in large intestine and used by intestinal flora. After passing through to the large intestine, raffinose is utilized by bifidobacteria, improving the propagation of bifidobacterium and producing short-chain fatty acid. So it can bring down the intestinal pH, increase humidity of faeces, and withhold harmful bacterium's multiplication. So it can be added to food ingredients as prebiotics. Raffinose also has certain protective effect on liver injury. It reduces formation of toxic metabolites by withholding harmful bacterium's multiplication, and then reduce hepatic detoxifying burden. Meanwhile, it has many physiological functions including anticancer, anti-inflammatory, decrease of serum cholesterol and immuno-enhancement. High-purity raffinose can be used as sweeteners in diet food with low-calorie. And it also can be used in the series foods for diabetics. In addition, as a nonionic surfactant, raffinose fatty glyceride, synthesizing with raffinose, has many features including high-security, minor irritant to the skin and low-allergia, therefore it can also be applied in cosmetic especially. With the characteristic above, raffinose is extensive in the fields of food, health products, medicine, daily chemical industry.
Raffinose is widely existed a variety of natural products, such as cottonseed, beets, leguminous plants, wheat and so on. With a high raffinose content in cottonseed and wheat germ, the content of cottonseed is about 4%˜9%, with the exact same as defatted wheat germ. Defatted wheat germ is the by-product after extraction of wheat germ oil. Underlying amount of wheat germ is up to 2,000˜2,500,000 tons every year in our country. As “the nutrition treasure house of human nature”, it has most abundant and high-quality protein, fatty, vitamins and minerals. People have been interested in its high nutritive, and constantly develop serial functional foods. The deep processing technology of wheat germ products is just starting out. Preparing high-purity raffinose from defatted wheat germ is significant in the acceleration of comprehensive utilizing wheat germ.
In present technology, the process for preparing high-purity raffinose from defatted wheat germ is that defatted wheat germ was immersed and extracted by high concentration alcohol-containing liquid to obtain raffinose, followed by decolorization, purification and refining of extracting solution. Wei Peipei (Wei Peipei, extraction and preparation of raffinose from defatted wheat germ, 2011, Jiangnan University, Wuxi) reported on a process for preparing high-purity raffinose from defatted wheat germ. Firstly, an extract is obtained by agitation leaching process from wheat germ, with agitation leaching for 2.5 hours by 75% aqueous alcohol at 50° C., with ratio of solid to liquid of 1:13. And the extracts rate of raffinose is 83.65%. Decoloration is operated in the system containing alcohols, with the best decolour conditions are pH 5.0, activated carbon concentration 4% (w/v), decoloring temperature 50° C., decoloring time 2 hours. Preliminary separating of raffinose by crystallization with the decolored solution, and raffinose can obtained by recrystallization.
The above process, the optimum total yield is 28.9% (raffinose content of defatted wheat germ is 7.95%), and the yield is not high. There are some problems with commercial scale, For example, large quantity of solvent in static method, low extraction ratio, long periods, extracting for several times and high requirement of equipment. High activated carbon consumption is used in the decoloring process, and hardly utilized repeatedly of activated carbon powder. The purity increase of raffinose is not ideal, the purity of raffinose is up to 98% after crystallization process for several times, which led to low recovery of raffinose. With the increase of crystallization time, industrial-scale and efficiency is limited.
Therefore, it still has some disadvantages in the prior art process for preparing high-purity raffinose from defatted wheat germ, not suitable for industrial-scale production, some improvement should do in the aspect of cost control, yield. Thus, process should be simplified and optimized based on technology that already exists, to seek a preparing method with simple process, low cost and high yield.